Temporal and spatial variation pf phosphate distribution in the sediment of a free surface water constructed wetland.

MAINE, M.A.; SUÑÉ, N.L.; HADAD, H.R.; SÁNCHEZ, G.C.

Ghent, Belgica

Simposio; International Symposium on Wetland Pollutant Dynamics and Control; 2005

Universiteit Gent, Faculty of Bioscience Engineering

This study is aimed at determining the spatial and temporal variation of the P distribution in sediments of an artificial wetland for sewage and industrial wastewater treatment, and the fraction that is potentially involved in the P exchange processes. Influent, effluent, macrophytes and sediment at the inlet, middle and outlet areas were sampled during 24 months. The P-fractionation in sediment was performed following the EDTA method, proposed by Golterman (1996). E. crassipes and T. domingensis carried out an efficient P removal when its cover was high, but E. crassipes caused anoxic conditions. Increase of cover of T. domingensis would contribute to attain oxic conditions and to improve P removal. When macrophytes are not present or their cover is low, sediment would increase its removal efficiency. A significant increase in the concentration of the fraction of Fe(OOH)»P and mainly that of CaCO3»P can be observed at the inlet. The high pH, Ca2+ and CO3-2 concentrations in the influent suggest that P would co-precipitate together with CaCO3. Therefore, it seems that CaCO3»P represents the main precipitating mechanism. However, mineralization of organic matter maintained the sediment at a pH range lower than the high values prevailing in the influent. CO3-2 would undergo partial dissolution and the released i-Pdiss would be readsorbed onto the Fe(OOH)»P fraction. Since the environment for P retention (high pH and Fe, Ca and ionic concentrations) is largely provided by the influent, the wetland would be expected to continue retaining P as far as the composition of the influent is maintained and there are available adsorption sites in the sediment.